In contemporary US evolutionism there are two main currents of thought. They are universal evolutionism of V.Gordon Childe and Leslie White and multilinear evolutionism of Julian Steward. This new twentieth-century perspective on the evolution of society is sometimes referred to as neo-evolutionism.
Julian Steward, an archeologist of Native American hunter-gatherer cultures, established a taxonomy for categorizing cultures based on the material evidence of their “social, political, and religious patterns” that were “empirically determined” by their “cultural core”. A society’s “cultural core” according to Steward was composed of a “constellation of features which are most closely related to subsistence activities and economic arrangements”–or in other words the natural and social environment. Steward called his study of the process of culture change “cultural ecology.” Cultural ecology is a term he coined to explain culture as an adaptation of a society to their environment. Like the evolutionists that preceded him, Steward believed that “significant cross-cultural regularities exist” among societies. However, unlike them Steward did not believe that these regularities are universal or progressive, from simple to complex, for all societies.
Leslie White, author of The Evolution of Culture: The Development of Civilization to the Fall of Rome (1959), approached the problem of identifying levels of progressive cultural evolution using his pre-anthropological background in science and physics. He subscribed to the 19th Century evolutionary theories of Lewis Henry Morgan and Edward B. Tylor and preferred to be called an “Evolutionist”. His model of social evolution is a progressive one that is based on levels of technological innovation rather than environmental adaptation. White claims that industrialized cultures and complex societies are more advanced because they have the capacity to harness more energy–”thermodynamics” than non-industrialized and simple societies (White 1959: 33). White even gives a hard science credibility to his theory by developing a mathematical formula for “culture process” that is now known as “White’s Law”: E x T > P, where E=energy, T=technology and P=product.
Elman Service, a former student of Julian Steward and a member of the neo-evolutionary group at Columbia University who called themselves the “Mundial Upheaval Society” claimed that social evolution was based on adaptations to the environment. In Origins of the State and Civilization: The Processes of Cultural Evolution (1975),
Service said the societies used an over-arching ideology to maintain social control and that the “earliest governments worked to protect, not another class or stratum of the society, but itself. It legitimized itself in its role of maintaining the whole society”. Service believed that government itself was a social adaptation that maintains a society with as a sort of Rousseau-like “social contract” of a shared ideology that maintains the hierarchy through reinforcement”, “leadership” and “mediation”.
Service believed that civilizations that fell were adaptive failures to a changing environment. They suffered from a “kind of failure of bureaucratic governance” by not being able to save its society from “external and internal threats to its integrity”
The Evolution of Political Society by Morton H. Fried, a student of Steward’s as well, is another foundational book of the Neo-evolutionism. The book, like the other neo-evolutionary works from the mid-Twentieth century, is dated in its language and socio-political context. However, Fried’s theories of how societies evolve over time, from small ones to big ones, and the “initiating conditions” that make each societal type possible (such as population increase, subsistence intensification, and so on) are just as relevant today as when the book was published way back in 1967.
Fried is careful to define his terms when describing the different factors of social evolution. For example, “’Authority’ is refers to the ability to channel the behavior of others in the absence of the threat or use of sanctions and “Power” is the ability to channel the behavior of others by threat or sanctions”. Another useful term re-defined by Fried that made understanding why some political systems are successful and some are not is “legitimacy”. Fried uses Weber’s categorization of two types of legitimacy based on how each is guaranteed: “internal legitimacy” is guaranteed via beliefs and values, and “external legitimacy” is guaranteed via social sanctions or force if customs or laws are broken.